Children ages 10 to 13 model the effect of greenhouse gases on Earth's atmosphere. Softballs represent the invisible infrared radiation emitted by the Earth as it is heated by sunlight. Armed with softball gloves and oven mitts representing greenhouse gases or embroidery hoops representing the inert gases nitrogen and oxygen, the children attempt to catch and throw the balls! They find that greenhouse gases such as carbon dioxide (CO2) and methane are uniquely shaped to catch and pass on infrared radiation, and so they are responsible for the warmth we enjoy on Earth. The children discuss how the addition of greenhouse gases by human activities leads to further warming and what steps we can take to slow it.
Introduce the activity as a game to model the greenhouse effect.
The Sun shining on Earth's surface provides enough energy for the average surface temperature to be about -2°F (-19°C).
- What warms Earth? The Sun. Some children may suggest that heat from within Earth adds warmth. Geothermal energy does contribute, but only a small amount. Radioactive decay of elements and gravitational energy inside Earth add less than 1% of the total energy on the surface; the Sun provides the rest.
Explain that they will play a game that models the greenhouse effect, a natural process that warms our Earth to about 57°F (14°C).
- Is the temperature here usually about 0°F? Or is it colder/warmer? Warmer.
Describe the activity as a model of how gases in Earth's atmosphere warm the surface from -2°F to an average of 57°F. Share that the Sun transfers some of its energy to Earth in the form of the sunlight we see (as well as some forms of radiation that we can't), warming Earth. Earth absorbs the sunlight and gives it back as an invisible form of energy, infrared radiation. The only thing keeping that energy from escaping back into space is the atmosphere. In the game, the children are gases in the atmosphere, and their goal is to keep the energy from escaping! Soft balls represent the infrared energy that is emitted from Earth's surface. Softball gloves, oven mitts, and embroidery hoops represent different gases in Earth's atmosphere. The balls are thrown up from the ground and the children must try to catch them using only the gloves, mitts, or hoops and carefully throw them to another child. Any balls that are not caught are lost into "space" and cannot be picked up again. The goal is to keep the balls in the air and passing between the children.
Much of the Sun's radiation is in the visible range of the electromagnetic spectrum, and for the most part, this type of light passes right through our atmosphere. It warms the surface of Earth, causing Earth to give off a radiation of its own: infrared radiation. The infrared radiation of Earth is invisible to us. Unlike the higher-energy radiation from the Sun, the low-energy, long-wavelength infrared radiation can't pass back through the atmosphere with ease. Some of it does manage to escape back into space, but most of it is captured by greenhouse gas molecules like water vapor, carbon dioxide (CO2), and methane. After a while, the gas molecules reemit the infrared energy, where it may be absorbed by another greenhouse gas molecule or Earth. The net result is warming.
Adapt your vocabulary to meet your audience's needs. Children in grades 5–8 are learning many of the points addressed in Catching a Heat Wave. They are learning that heat and light are associated with energy and that energy can be transferred from one substance to another. They are learning that light has a range of wavelengths, including visible and infrared. Tailor your discussions to the level of vocabulary they find comfortable.
Distribute the softball gloves, oven mitts, and embroidery hoops randomly to the group (one per person). Throw the balls up from the ground and allow the controlled mayhem to ensue!
Allow the children 5 to 10 minutes to toss the balls. Moderate the activity to ensure that dropped balls do not reenter the game.
Regather the group and invite the children to look at the tags on their gloves, mitts, or hoops. Share that just like these tools, gases in the atmosphere all have different shapes, which allow them to catch infrared energy well or not at all.
- Our atmosphere is made up mostly by what gases? Nitrogen and oxygen.
- What tool represented these gases? Embroidery hoops.
- How well did the hoops work in catching the balls? What does that say about the shape of nitrogen and oxygen gases for catching infrared radiation? They did not work well; they are the wrong shape to catch infrared energy.
- Which tools were the best shapes for keeping the balls in motion? The softball gloves and oven mitts.
All molecules are able to absorb and emit light energy, but at the molecular scale, that light has to have just the right amount of energy for a particular type of molecule to absorb. Greenhouse gas molecules are all made up of at least three atoms bonded together. They are able to absorb infrared radiation because its energy is just right for causing the atoms of the molecules to move slightly in relation to each other, or vibrate. (The visible light from the Sun was too energetic for the molecules to "catch.") The molecules then emit the energy as infrared radiation, which is often caught by another greenhouse gas molecule or the surface of Earth.
Explain that molecules of carbon dioxide gas are fairly effective at catching infrared energy emitted by Earth. Methane is very effective at catching infrared energy. Methane comes from natural wetlands, but our farm animals and rice paddies also add it to the atmosphere. After a while, the gases let the infrared radiation go again, where it can be caught again by other greenhouse gases or sent back to Earth's surface.
- If we invited more people to play, what would you have them use to keep the balls moving? Softball gloves and oven mitts.
- What gas did the oven mitts represent? Carbon dioxide or CO2.
- Has anyone seen, eaten, or breathed carbon dioxide? Where do we find carbon dioxide? Yes! We all have! Carbon dioxide makes soda pop bubble. It's in the air we breathe. In its solid form, we see it as dry ice.
- Where does carbon dioxide in our atmosphere come from? Cars, power plants, factories, and volcanos.
Share that scientists may not be able to see the gas molecules, but they are able to measure how much of each type is in the atmosphere.
- Did the carbon dioxide/gloves and methane/mitts keep the infrared radiation/balls from escaping into space?
- If infrared energy coming up from Earth isn't caught by a gas molecule, where does it go? Up into space.
- What would happen if there were no softball gloves (carbon dioxide) or oven mitts (methane)? All the infrared energy would escape into space. Earth would be cold! Carbon dioxide and methane keep the energy trapped in Earth's atmosphere — keeping us warm!
- What would happen if there were more softball gloves? More balls (infrared energy) would be kept in play — it would be warmer.
- Are gas molecules as big as softball gloves, oven mitts, and embroidery hoops? Can we see them? No, they are too small to see.
Share the Carbon Dioxide in Earth's Atmosphere chart with the children.
- What does the graph show? That carbon dioxide levels have been rising since about 1850.
- What do the children predict will happen in their lifetimes to the level of carbon dioxide, based on the shape of the curve? The carbon dioxide levels will continue to rise.
The amount of carbon dioxide in Earth's atmosphere, and Earth's temperature, have fluctuated in a cyclical pattern through time. These cycles of cooling and warming are natural, and caused, over the last 750,000 years, primarily by cyclic changes in Earth's orbit. During that time frame we have experienced alternating periods of warmth and periods of glaciations. However, at present, the levels of carbon dioxide in the atmosphere far exceed even the highest levels of the past half-million years. Our global temperature is increasing in response to this added greenhouse gas.
The blue curve shows how the amount of carbon dioxide in our atmosphere has changed over the last 400,000 years, and the red curve shows how Earth's temperatures have changed over that same time. Together, the curves show that Earth's temperatures are warmer when there is more carbon dioxide in the atmosphere. Ice cores and other data, like tree rings and sediment cores from the ocean floor, provide the evidence for this cyclical pattern through time.Today's levels of carbon dioxide far exceed even the highest levels of the past half-million years. Our global average temperature is increasing in response to this added greenhouse gas. Image courtesy of the UN Intergovernmental Panel on Climate Change (IPCC), Third Assessment Report, Climate Change 2001.
The carbon dioxide concentration in the atmosphere has been measured directly since 1957. The instruments at Mauna Loa, Hawaii, reflect the seasonal uptake and release of carbon dioxide by plants as "wiggles," but show an overall sharp increase.
Explain that scientists have been measuring the amounts of carbon dioxide and methane in the atmosphere and they are going up very quickly. If there were 10,000 people playing the game, most would need to be armed only with embroidery hoops to really represent our atmosphere. Only four would have softball gloves to represent carbon dioxide — that doesn't seem like very many! Yet those four would keep catching and throwing infrared radiation balls for 50 to 200 years — that's how long carbon dioxide stays in our atmosphere! Burning fossil fuels adds about 30 billion metric tons of carbon dioxide to the air each year— that's a lot of extra softball gloves!
The amount of carbon dioxide in Earth's atmosphere has been directly measured at Mauna Loa, Hawaii, for half a century. The data reflects a sharp increase in carbon dioxide to levels higher than our Earth has experienced in the past half-million years — and certainly higher than humans have ever experienced. The seasonal uptake and release of carbon dioxide by plants in the northern hemisphere were captured here as "wiggles." Image courtesy of Robert A. Rohde/Global Warming Art.
- What does that extra carbon dioxide do with infrared radiation emitted by Earth? Keeps it from escaping into space and lets it go, where it can be caught by other greenhouse gases or Earth's surface.
- What effect do you think that trapped radiation might have on Earth's temperatures? They become warmer.
Share the Global Temperature Change chart with the children.
Share with the children that many factors influence the Earth's temperatures, including the amount of energy reaching the Earth's surface from the Sun, the amounts of natural greenhouse gases, and how all of Earth's water, geological, and other cycles interact. Volcanos often make powerful explosions of carbon dioxide and ash, and they have helped shape Earth's climate over time. Some of the temperature rise they see in the graph is caused by the Sun. However, most scientists agree that the warming is mostly due to the carbon dioxide our activities have added to the atmosphere.
- What is the graph about? Earth's temperature between about 1860 and the year 2000.
- What does the graph show? That Earth's temperatures have been rising or getting hotter since about 1900.
- What are some of the effects of Earth's temperatures rising? Our climate is getting warmer. Glaciers and sea ice are melting.
- What do the children predict will happen in their lifetimes, based on the shape of the curve? The temperature will continue to rise.
Earth's global surface temperatures are rising at an unprecedented rate. The past century has seen an increase of a little more than 1°F (0.74°C). Today's global temperatures are the highest of the past 500 years, perhaps even for the past millennium. The scientific consensus is that the warming is due to greenhouse gases emitted as a result of human activities.
Earth's temperatures are shaped by various natural factors that interact to warm or cool the climate. Changes in Earth's orbit, in addition to less influential changes in the Sun's intensity, outgassing from volcanos and other sources, and changes in ocean currents, have resulted in long-term cycles of cooling and warming. While these influences are still not fully understood, the majority of scientists agree that their effects are minor compared to the contributions of human activities. Changes in solar intensity and volcanos produced most of the warming from preindustrial times to 1950, but are not implicated in the current global change. For instance, when Mt. Pinatubo erupted in 1991, the global average temperature dropped by 0.9°F (0.5°C) as volcanic particles in the air reflected some of the Sun's energy. (The volcano also released carbon dioxide, a warming agent, but this addition is thought to be small compared to human contributions.) Studies by the National Center for Atmospheric Research (NCAR) attribute less than one-third of the current warming to changes in the Sun's intensity.
Trees are great at taking carbon dioxide out of the atmosphere — they use it to make their own food to grow. Taking care of our forests helps the trees continue to use up this greenhouse gas. Scientists and engineers are researching other ways to take the extra carbon dioxide out of the air.
- In terms of the game, what can we do to help our Earth from getting too hot? Take away softball gloves and oven mitts or keep more from coming to play.
- What can we do in the real world? Take carbon dioxide and methane out of the atmosphere.
- What are some ways we can add less greenhouse gases to the air? Walk or carpool instead of asking for a ride. Replace regular light bulbs with compact fluorescent bulbs. Save energy! By turning off computers, TVs, and game consoles when they're not in use, we use less electricity, which comes from power plants that usually burn coal. Eat less meat.